The present invention relates to a method for allocating a radio channel to be used in a microcellular system (MCS) of a portable telephone set which shares a frequency band with a cellular mobile telephone system (CMTS).
In the prior art, the allocation of a control channel and a speech channel in the MCS which shares the frequency band with the CMTS are carried out in the same system and configuration as those of the CMTS so that the CMTS is locally reduced in scale (which is commonly called as a cell split).
However, the prior art method includes the following problems.
1. When an MCS is to be installed in an area, reallocation of frequencies including those for neighboring CMTS's is required.
2. When a plurality of MCS's are to be arranged three-dimensionally in a multi-flow building, a frequency allocation plan is difficult to attain.
Accordingly, the frequency allocation to the MCS which shares the frequency band with the CMTS is very difficult job.